Question

I have a table which includes all the users video downloading history:

src_ip   vlan_id  video_id area  date_pl
aaaa     A        1        123   xxxx-xx-xx
aaaa     A        2        123   xxxx-xx-xx
aaaa     B        1        456   xxxx-xx-xx
bbbb     A        4        123   xxxx-xx-xx
bbbb     C        6        567   xxxx-xx-xx
...

I use the combination of src_ip and vlan_id to identify different users, Now I want to randomly select 50 different users (which means 50 distinct combinations of src_ip and vlan_id )and list all their downloading history.

So first I did:

   SELECT distinct src_ip, vlan_id from video_2 as table2 
   WHERE date_pl >= '2011-11-29 00:00' AND date_pl <= '2011-12-05 23:55' order by rand() limit 50

Then I did:

   SELECT src_ip, vlan_id, video_id, area from video_2 
   where video_2.src_ip = table2.src_ip AND video_2.vlan_id = table2.vlan_id 
   AND date_pl >= '2011-11-29 00:00' AND date_pl <= '2011-12-05 23:55'

But the problem is, since they are two independent queries, in the second query, it doesn’t know what table2 is.

How can I solve this problem or how to merge these two queries into one?

Answer 1

CREATE TEMPORARY TABLE table2
AS
SELECT distinct src_ip, vlan_id from video_2
WHERE date_pl >= '2011-11-29 00:00' AND date_pl <= '2011-12-05 23:55'
ORDER BY rand() 
LIMIT 50;

SELECT src_ip, vlan_id, video_id, area
FROM 
   video_2
   JOIN 
   table2 ON video_2.src_ip = table2.src_ip AND video_2.vlan_id = table2.vlan_id';

You can can’t make “table2” derived in line because of restrictions on the use of LIMIT in subqueries. Otherwise it’d be

SELECT 
   v2.src_ip, v2.vlan_id, v2.video_id, v2.area 
FROM 
   video_2 v2
   JOIN 
   (SELECT distinct v.src_ip, v.vlan_id from video_2 v
   WHERE v.date_pl >= '2011-11-29 00:00' AND v.date_pl <= '2011-12-05 23:55'
   ORDER BY rand() 
   LIMIT 50
   ) table2 ON v2.src_ip = table2.src_ip AND v2.vlan_id = table2.vlan_id;

Edit: Restrictions LIMITs in subqueries apply to IN mostly, not derived tables

Edit 2: added more aliases